The present invention relates to the field of prevention and treatment of graft-versus-host disease using interleukin-12.
An individual mammal's immune system functions through recognition of certain cell surface proteins, some of which are termed major histocompatibility complex proteins, or MHC proteins. Additional minor histocompatibility proteins exist which can also contribute to immunological recognition events, The individual mammal's immune system recognizes its own MHC proteins, or those of its identical twin, as self and thus does not destroy its own cells or those of its identical twin. Members of the same species may share major and/or minor histocompatibility antigens, and thus an individual may not recognize the cells of another member of its species as non-self, depending on the degree of the differences between the MHC proteins of the two individuals. When an individual's immune system recognizes the cells of other members of the same species as non-self, the first individual's immune system may proceed to destroy the cells of the second individual. In humans, the major histocompatibility proteins are known as "HLA" antigens.
When tissues such as bone marrow, blood cells, or solid organs are transplanted from one individual to another, normally the recipient will recognize the donor's cells as non-self and the recipient's immune system will destroy the donor's cells as described above. For this reason, in a tissue transplantation, the recipient is normally subjected to immunosuppressive drugs and/or irradiation. However, transplantation patients are also subject to immunologic recognition in the opposite direction, that is, the donor tissue may contain immunologically competent cells which proceed to destroy the recipient's cells, a condition termed "graft-versus-host disease" or "GVHD".
At the present time, many leukemia and lymphoma patients are treated by bone marrow transplantation. When an identical twin is available, such transplantation is termed "syngeneic" since the genetic characteristics of donor and recipient are identical. More frequently, bone marrow transplantations are "allogeneic", that is, the bone marrow which is transplanted is donated by an individual whose genetic characteristics differ from those of the recipient, especially as regards the MHC and minor histocompatibility antigens expressed on the surfaces of each individual's cells. Allogeneic bone marrow transplantation is being performed more and more frequently. In 1990, more than 4,000 such transplantations occurred. In recognition of the increasing need for bone marrow donors compatible with potential recipients, an international marrow donor registration system has been developed, in order to provide phenotypically matched marrow from unrelated donors.
Concomitant with the increasing frequency of allogeneic bone marrow transplantation, the incidence of potentially fatal complications such as graft-versus-host disease is also increasing. Graft-versus-host disease can develop when bone marrow, blood products, or solid organs containing immunocompetent cells are transferred from a donor to a recipient. Thus, when MHC antigenic differences exist between the donor and recipient, the recipient is at risk for the development of graft-versus-host disease. Graft-versus-host disease may also develop when there are antigenic differences between donor and recipient for the minor histocompatibility antigens. Thus, graft-versus-host disease can also develop between MHC-matched persons. Moreover, surgery patients who receive directed blood transfusion, for example, transfusion of blood from an HLA homozygous child to a heterozygous parent, may also develop graft-versus-host disease.
Presently graft-versus-host disease is inhibited by attempting to eliminate immunocompetent donor cells, for example, by in vitro manipulation of the donor bone marrow. For example, immunocompetent T cells may be removed from the donor bone marrow through physical separation such as by lectin agglutination, or by treatment of the bone marrow with monoclonal antibodies directed to T cells. However, use of bone marrow depleted of T cells is associated with a higher rate of graft failure, which is frequently fatal. Use of T cell depleted bone marrow grafts is also associated with an increased incidence of relapse among the recipients, particularly recipients having chronic myelocytic leukemia.
In another approach, the recipient is subjected to immunosuppressive therapy after transplantation. Such immunosuppression may occur by use of glucocorticoids, cyclosporin, methotrexate, or combinations of such drugs. However, immunosuppression results in increased incidence of infection, and even when immunosuppressant drugs are used, graft-versus-host disease may still occur.
Interleukin-12 is a heterodimeric cytokine which was originally identified as a factor which induces .gamma.-interferon from T cells and natural killer cells as set forth in PCT/US91/06332, published Apr. 2, 1992, which is incorporated herein by reference. PCT/US91/06332 refers to interleukin-12 as Natural Killer Cell Stimulating Factor or NKSF. EP 433827, published Jun. 26, 1991 discloses interleukin-12 as a cytotoxic lymphocyte maturation factor (CLMF). The amino acid sequences of the human interleukin-12 subunits are set forth in SEQ ID NO: 1/SEQ ID NO: 2 (40 kD subunit) and SEQ ID NO: 3/SEQ ID NO: 4 (35 kD subunit).
Interleukin-12 also stimulates natural killer cells in vitro by increasing their ability to lyse target cells at a level comparable to that obtained with interferon-.alpha. and interleukin-2, well-known activators of natural killer cells' cytotoxic activity. Additional in vitro activities of interleukin-12 which have been identified include induction of T cell proliferation as a co-stimulant; suppression of interleukin-2 induced proliferation of natural killer blasts; suppression of interleukin-2 induced proliferation of T cell receptor-.gamma..delta.-positive cells; promotion of Th1 T cell differentiation from progenitors; enhancement of Th1, but not Th2 proliferation; enhancement of T cell cytolytic activity; enhancement of cytotoxic lymphocyte generation; enhancement of natural killer and natural killer blast cytolytic activity; ex vivo enhancement of natural killer activity in peripheral blood mononuclear cells of interleukin-2-treated patients; induction of adhesion molecules on natural killer cells; induction of perforin and granzyme B mRNAs in natural killer blasts; induction of interleukin-2 receptor subunits (p55, p75) on natural killer cells; induction of low levels of tumor necrosis factor-.alpha.; suppression of IgE synthesis by interferon-.gamma.-dependent and independent mechanisms; modulation of T cell development in fetal thymic organ cultures; and synergy with kit ligand to promote growth of myeloid and B cell progenitors. The known in vivo activities of interleukin-12 include induction of interferon-.gamma.; enhancement of natural killer cell activity in spleen, liver, lungs and peritoneal cavity; enhancement of generation of allo-specific cytotoxic lymphocytes; induction of extramedullary hematopoiesis in mouse spleen; reversible suppression of hematopoiesis in bone marrow; reversible induction of anemia, lymphopenia, and neutropenia in mice; suppression of anti-IgD induced IgE, IgG1, and interleukin-4 expression; increased survival in SCID mice treated with Toxoplasma gondii; cure of leishmaniasis in susceptible strains of mice; decreased bioburden in cryptococcoses model; suppression of tumor growth; and promotion of immunity to tumor cells. Interleukin-12 is also induced in vivo in the shwarzman reaction model of septic shock.
From the known activities of interleukin-12, it would be expected that treatment of mammals in allogeneic bone marrow transplantation would result in more severe graft-versus-host disease. Both interferon-.gamma. and tumor necrosis factor-.alpha., which are induced by interleukin-12 treatment, have been implicated in producing graft-versus-host disease. Furthermore, cytotoxic T-lymphocytes, whose generation is enhanced by interleukin-12, have also been implicated in graft-versus-host disease pathophysiology. Murine studies have shown that inhibition of a Th1 response by treatment with interleukin-2 is associated with inhibition of graft-versus-host disease. Therefore, enhancement of Th1 responses by treatment with interleukin-12 would be expected to increase the severity of graft-versus-host disease.